As a human perspires, the perspiration preferably evaporates to cool the skin by evaporative cooling. However, as is well known, many materials that come in contact with the body prevent moisture from freely accessing the atmosphere and evaporating. To many people, the attribute of conveying moisture away from the skin is referred to when describing whether or not a fabric "breaths". Clearly, this is a well known attribute and one in which much effort has been placed to acquire.
However, there are many situations where garments or materials must also be water proof or possess some other important attribute which is opposite to the kind of open structure one envisions when thinking of a material that "breaths". For example, gloves and boots are often required to be impervious to liquids. In addition, boots and shoes are normally relatively closed structures for durability. These apparel articles are most notorious for not being able to breath.
In the above referenced patent application, a material comprised of a combination of two different types of fibrous materials was described for use in bed pads. The material has proven to be highly wickable carrying substantial amounts of fluid away from the patient. One important characteristic of the foregoing described fabric is its exceptional ability to transport moisture laterally through the pad. In trying to apply the material in the foregoing patent application to other uses, several unforeseen shortcomings have been found.
A first unforeseen problem relates to the desirability to utilize the fabric in a bonded structure such as a laminated article. In one arrangement, it was desired to bond the fabric to polyurethane foam. However, the polyurethane was wicked into the interstices of the fabric and rendered the lateral transport of moisture totally ineffective. In essence, the fabric's virtue caused this problem.
A second problem was encountered when the fabric was bonded to laminate materials on both sides to form a sandwich around the fabric. The fabric has pretty good strength to hold up to repeated washings and other abuse; however, there is a limit to its strength. It was found that the laminated structure was prone to delamination within the fabric. Essentially, the fabric becomes disentangled and this weakness in the structure of the fabric becomes most apparent when the laminated layers are rather cohesive such as a plastic film. In this arrangement, one can peel apart the laminated structure leaving part of the fabric bonded to one laminate material and the other part of the fabric bonded to the other laminate. The same general problem of the laminated structure is that is similarly susceptible to shear forces along the fabric boundary. As a shoe insert, the laminate could very well be subjected to substantial shear forces along the boundary layer.
Clearly, these problems are going to limit the usefulness of a fabric that has some very good moisture handling properties. Accordingly, it is an object of the present invention to develop a fabric design that will provide the positive attributes of the spunlaced fabric but which overcomes the drawbacks and problems as described above. It is a more particular object of the present invention to provide an improved, more robust fabric design that is suited for bonding to other materials while retaining the moisture absorbency and lateral conduction of moisture.